This invention relates to selective synthesis and catalysts therefor.
According to the invention an allylic compound is reacted with an organozinc compound Zn(R6)2 to eliminate a group (the leaving group) from the allylic compound and to add a group from the organozinc compound to it in the presence of a copper salt catalyst and a chiral organic ligand for the copper. Preferably the ligand is a primary or secondary amine in which the nitrogen atom is directly linked to the chiral centre. The allylic compound is suitably of formula 
where X is the leaving group for example a chlorine atom and in which A is hydrogen or an alkyl or aryl group, preferably having 1-20 carbon atoms. If substitution occurs at the carbon atom marked * a chiral centre may be formed. This process is known as Sn2xe2x80x2 substitution; an alternative substitution at the carbon atom marked xe2x80xa0 may occur in which case there may be no chiral centre, this process is known as Sn2 substitution.
The reactions are shown as follows: 
where R6 is a group from the organozinc compound. Surprisingly, in this process the former reaction is generally favoured and is influenced by the leaving group, ligands and solvents as shown below, tetrahydofuran being a particularly favourable solvent. The process is normally chemoselective for Sn2xe2x80x2 substitution and/or stereoselective.
In a preferred form of the invention the reaction is as shown below: 
R1-R6 are alkyl, alkenyl, alkynyl, aryl, aralkyl or heterocyclyl groups optionally substituted by for example halogen, alkoxy, aryloxy, acyloxy, nitro, amide, acetamide, carboxylate, cyano, acetal, sulphide, sulphonate, sulfone, sulfoxide, phosphite, phosphonate, phosphine groups, each preferably having at most 20 and preferably less than 10 carbon atoms, or R1 to R5 may be H, R7 is an aryl for example a phenyl or ferrocenyl or substituted aryl or ferrocenyl group of which the substituents may be for example 1-aminobenzyl, 1-amino-2-naphthylmethyl, 1-amino-(4-tert-butylphenyl)methyl, trimethylsilyl, phosphite, phosphine, alkyl, alkoxy, thiophosphonate, amino and/or halogen (eg Cl or Br) atoms and R8 is an alkyl or aryl, preferably a methyl, ethyl, propyl, tert-butyl, phenyl or naphthyl for example 2-naphthyl group which may be substituted for example by nitro, alkoxy, alkyl and/or haloalkyl group. X is halogen, OR9, OCOR9, OCO2R9, OSO2R9, OCS2R9 CH(OR10)2, OPO(OR9)2, SOR9, or SO2R9 where R9 and R10 are optionally substituted C1-C10 alkyl or aryl, of which the substituents may be halogen, nitro, methoxy, trifluoromethoxy, methyl, ethyl, tert butyl or sulphonate groups e.g. methyl, ethyl, trifluoromethyl, phenyl, tosyl, p-bromophenyl, p-nitrophenyl, p-methoxyphenyl, or R7 and R8 may together form a 5 or 6 membered carbocyclic or heterocyclic ring providing that a carbon atom to which the nitrogen is attached is chiral. for example R7 and R8 together may be 1-indane, bornylamine or 2-cyclohexylamine. Y is halogen, carboxylate for example, acetate, acetoacetate, cyanide, or thiocyanate and Z is an ether or thioether for example dimethylsulfide, tetrahydrofuran or diethylether. Preferably R1-R2 and R3 and one of R4 or R5 are H and the other one of R4 or R5 is aryl, for example phenyl, 4-chlorophenyl or 4-trifluoromethyl phenyl or is a trialkyl (e.g. tri-isopropyl) silyl oxymethyl groups R6 is alkyl, tri-alkyl (e.g. trimethyl) silyl methyl, phenyl or 2,2-dimethylbut-3-enyl. R7 is ferrocenyl, R8 is naphthyl, X is chloride, Y is chloride or bromide and Z is dimethylsulfide. R5 is preferably phenyl and R6 is preferably neopentyl. The substituents of R7 preferably have at most 10 carbon atoms in total and those of R8 preferably at most 8 carbon atoms in total. Alkanes, cyclo alkanes and/or aromatic solvents for example toluene may be present.
Preferred solvents are ethers for example diethylether, 1,4-dioxane, tertbutylmethylether and especially tetrahydrofuran. Preferred temperatures are xe2x88x92120xc2x0 C. to 25xc2x0 C. more preferably xe2x88x92100xc2x0 C. to 20xc2x0 C. and especially xe2x88x9290xc2x0 C. to xe2x88x9250xc2x0 C.
Preferred concentrations of catalyst are 0.1 atom % to 20 atom %, especially 0.5 atom % to 5 atom % expressed as copper atoms based on moles of the allylic compound.
The ratio of copper atoms to the amine ligand molecules is suitably 1:10 to 2:1.
Compounds for formula 
in which A is a ferrocenyl or substituted ferrocenyl group and B is a group R8 other than a methyl or phenyl group are believed to be novel. The groups A and B should be different in order to obtain stereospecificity. B is preferably a 2-naphthyl group.